Charge trapping nonvolatile semiconductor memories using a charge storage insulating film for charge trapping as a charge storage layer have been proposed (see Jpn. Pat. Appln. KOKAI Publication No. 2004-71877). In this type of charge trapping nonvolatile semiconductor memory, electric charges injected through a tunnel insulating film into the charge storage insulating film are trapped at a trap level in the charge storage insulating film, and thereby stored in the charge storage insulating film. As a typical charge trapping nonvolatile semiconductor memory, a MONOS-type nonvolatile semiconductor memory is known, and a silicon nitride film is typically used as the charge storage insulating film.
However, it is not necessarily appropriate to suggest that excellent charge storage insulating films can be achieved conventionally, and it is not appropriate to suggest that non-volatile semiconductor memories excellent in both writing/erasing characteristics and charge retention characteristics are obtained conventionally.